The tiny skeleton discovered on the Isle of Skye, called Bellairsia gracilis, is just 6cm long and dates from the Middle Jurassic period, 166 million years ago. The exceptional new fossil consists of an almost complete skeleton in living articulation, missing only the snout and tail. This makes it the most complete fossil lizard of this age anywhere in the world. Bellairsia has a mixture of ancestral and modern features in its skeleton, providing evidence of what the ancestor of today’s lizards (which are part of a wider group of animals known as “squamates”) may have looked like.
The joint project of researchers at the universities of Warsaw, Oxford and UCL. First author Dr Mateusz Talanda (University of Warsaw and UCL) said: “This small fossil allows us to see evolution in action. Rarely in paleontology do you have the opportunity to work with such complete, well-preserved fossils from a time we know so little about.’ The fossil was found in 2016 by a team led by the University of Oxford and the National Museum of Scotland. It is one of several new fossil discoveries from the island, including early amphibians and mammals, that reveal the evolution of important animal groups that persist into the present day.
Dr Talanda commented: “Bellairsia has some modern lizard features, such as features related to cranial kinesis – that is the movement of the skull bones in relation to each other. This is an important functional feature of many living squamates.” Co-author Dr Elsa Panciroli (Oxford University Museum of Natural History and National Museums Scotland), who discovered the fossil, said: “It was one of the first fossils I found when I started working on Skye. A small black skull stuck out of the pale limestone, but it was so small that I was lucky to catch a glimpse of it. When I looked closer, I saw tiny teeth and realized I had found something important, but we had no idea until later that almost the entire skeleton was there.”
10,000 more species
Squamates are a living group that includes lizards and snakes and today includes more than 10,000 species, making them one of the richest groups of living vertebrates. They include animals as diverse as snakes, chameleons and geckos found all over the world. The group is characterized by numerous specialized characters of the skull and the rest of the skeleton. Although we know that the earliest origin of pangolins lies 240 million years ago in the Triassic, the lack of fossils from the Triassic and Jurassic makes it difficult to trace their early evolution and anatomy.
Analysis of the new fossil alongside living and extinct fossil pangolins confirms that Bellairsia belongs to a “tribe” of the pangolins family tree. This means that it split off from other lizards just before modern groups arose. The research also supports the finding that geckos are a very early branch line, and that the mysterious Oculudentavis fossil, previously thought to be a dinosaur, is also a scaly lineage.
To study the sample, the team used X-ray computed tomography (CT), which, like medical CT, enables non-invasive 3D imaging. This allowed the scientists to view the entire fossil, although most of the specimen is still hidden by the surrounding rock. While medical scanners work on a millimeter scale, Oxford University’s CT scanner revealed details down to a few tens of micrometers. Parts of the skeleton were then imaged in even greater detail, including the skull, hind limbs and pelvis, at the European Synchrotron (ESRF, Grenoble, France). The intensity of the synchrotron beam enables a resolution of 4 micrometers, revealing the details of the smallest bones in the skeleton.
Co-author Professor Roger Benson (Department of Earth Sciences, University of Oxford) said: “Fossils like this Bellairsia specimen are of enormous value in filling gaps in our understanding of the evolution and history of life on Earth. Previously, it was almost impossible to study fossils as tiny as this, but this study shows the power of new techniques including CT scanning to image them non-destructively and in great detail.” Co-author Professor Susan Evans (UCL), who first described and named Bellairsia 25 years ago from several jaw bones and a skull from Oxfordshire, added: “It’s amazing to have a complete specimen of this exciting little lizard and see where it fits into the evolutionary tree. Through fossils like Bellairsia, we gain a better understanding of early lizard anatomy. Angus Bellairs, the lizard embryologist after whom Bellairsia was originally named, would be delighted.’
The study was led by Dr. Mateusz Talanda (University of Warsaw) and involved scientists from Oxford University’s Department of Earth Sciences, Oxford University Museum of Natural History, UCL (University College London), European Synchrotron Radiation Facility, Natural History Museum London and National Museum of Scotland. Funding was provided by the Ministry of Science and Higher Education, Poland. The John Muir Trust provided access to the Site of Special Scientific Interest on the Elgol Coast and NatureScot granted permission to collect the fossils.
Source Reference: Mateusz Tałanda and Vincent Fernandez et al. Synchrotron tomography of a stem lizard elucidates early squamate anatomy. Nature, 2022; DOI: 10.1038/s41586-022-05332-6
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